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New tools and off-season planning facilitate IPM for onion thrips

New insecticides effectively control onion thrips. Applying these as part of a planned rotation of threshold-based sprays can control thrips, save money and prolong the life of these effective chemistries.

Posted on December 17, 2012 by Ben Werling, Michigan State University Extension

New insecticides, including
Movento and Radiant, can be used as part of an effective integrated pest management (IPM) program to
control onion
thrips, a damaging pest of Michigan onions. Off-season planning can help
growers use these compounds effectively and prolong their useful life. Keys to
success include planned rotation, appropriate application and the use of
research-based thresholds.

Planning a rotation prior to the growing season can ensure
that these new chemistries are applied at the right time and rotated with other
chemical classes to reduce resistance. Planning a rotation involves sketching
out a sequence of insecticide applications for the worst-case scenario, where
thrips populations exceed threshold each week of the growing season. The key is
to include a sequence of compounds with different modes of action, which should
delay development of resistance.

Example of a rotation of insecticides with different modes
of action;
at each week, thresholds can be used to decide if application is
necessary.

When formulating a rotation, plan to apply the same compound
in back-to-back weeks if threshold is exceeded after the first application; do
not space applications of an individual product out across the growing season.
This limits the application of a given insecticide to one thrips generation, which
lasts two to three weeks, and avoids selecting multiple generations for
resistance. Second, plan to use insecticides when they will be most effective.
For example, Movento
should only be applied at the start of the season, while compounds such as Radiant
are effective at knocking back high populations that build later. (Final
registration of Movento for onions is currently pending after a 2012 Section 18
exemption.)

Planning for effective application is also important. Work
by Dr. Brian Nault
of Cornell University recently presented
at the Great Lakes Fruit and Vegetable Expo
shows that using a penetrating surfactant is essential when applying insecticides
in onions. Further, his work suggests it is important to avoid tank-mixing
these products with chlorothalonil-based fungicides, as it compromises these
insecticides’ effectiveness.

Once a rotation is planned, action thresholds can
inform decisions about whether to apply an insecticide at a given point during
the growing season. For example, Dr.
Zsofia Szendrei of Michigan State University
has observed that after applying back-to-back applications of Movento, it may
be possible to skip one to two weeks of insecticide applications, as its systemic
nature means it has longer residual activity. Dr. Szendrei’s ongoing work
shows that using thresholds may reduce insecticide applications and save money while
providing control as effective as calendar-based spray schedules.